1. Field Of The Invention
The invention pertains to sealed packages and, more specifically, to an improved, sealed blister package for securing products therein prior to use and to a method for sealing products in a blister package.
2. Description Of The Prior Art
Sealed blister containers for holding products have been proposed, and such containers are useful for holding products, such as pre sterilized medical devices, that must be isolated from the environment prior to use due to the ability of the containers to be hermetically sealed. Illustrative blister containers for holding sterile medical devices are shown in U.S. Pat. Nos. 4,324,331 to Ignasiak and 4,216,860 to Heimann and, generally, include an open, relatively rigid blister tray having a peripheral flange and a channel formed interiorly of the peripheral flange for receiving a pre-sterilized medical device. One or more foam plugs are positioned in the channel at discrete locations to hold distinct parts of the medical device against the tray and inhibit movement of the medical device within the container prior to use. A paper backing sheet is positioned over the open tray in overlapping engagement with the peripheral flange and the plugs and is continuously sealed or bonded to the tray along the peripheral flange to close the tray, maintain a sterile environment therein and urge the plugs toward the parts of the medical device being held against the tray. Additionally, the backing sheet is bonded directly to the plugs to permit the container to be opened by manually peeling away the backing sheet with the plugs attached thereto, such that the medical device can be dropped freely from the container onto a sterile field without manual contact with the medical device itself. The sealing process typically involves thermally compressing the backing sheet against the flange and plugs to bond the backing sheet to the flange and plugs, respectively. Because the plugs are located interiorly of the peripheral flange at discrete locations, the backing sheet must be compressed at multiple, distinct areas producing tensile stresses in the paper backing sheet that could tear or weaken the backing sheet. Furthermore, the foam plugs are contained entirely within the peripheral confines of the channel and move downwardly in the channel when the backing sheet is compressed against the plugs due to the open cell characteristics of foam. Therefore, the backing sheet must be compressed against the plugs with compressive forces significantly greater than required to be exerted against the relatively rigid peripheral flange to bond the backing sheet to the plugs. The requirement for relatively high compressive forces detracts from the efficiency of the sealing process and can produce an unequal force distribution in the backing sheet resulting in structural impairment thereof. Even when the required high compressive forces are uniformly applied, the backing sheet nonetheless frequently fails to bond to the plugs due to the plugs being able to move considerably downwardly within the channel when the backing sheet is compressed thereagainst, and the unbonded plugs can drop onto the sterile field along with the medical device when the backing sheet is peeled from the tray. Consequently, conventional blister containers usually employ a coating on the backing sheet to facilitate thermal bonding, and the coating must be applied to the backing sheet at each of the distinct sealing areas for the plugs. The need for thermal bonding facilitating coatings significantly complicates the sealing process and commonly fails to enhance bonding of the backing sheet to the plugs. Failure of the backing sheet to bond to the plugs can not be visually discerned because the interface of the backing sheet and the plugs is concealed entirely from view by the backing sheet and the plugs, respectively. Proper bonding of the backing sheet to the plugs is, therefore, difficult to ascertain after the backing sheet has been applied and has a negative impact on quality control.
A further drawback to conventional sealed blister containers is that failure of the backing sheet to bond to the plugs allows the plugs to move within the containers subsequent to the containers being sealed along the peripheral flange. Accordingly, the plugs are rendered ineffective in holding a medical device against the tray, and the medical device can shift and move within the container during shipping and handling prior to use. Movement of the medical device within the container prior to use is undesirable because the medical device can be damaged, and relatively fragile medical devices are particularly likely to be compromised by such movement. Prior art blister containers secure the plugs against movement within the container by forming the tray with specially configured walls adjacent the plugs to inhibit movement of the plugs and, therefore, the medical device, within the channel. Because different medical devices must be held by the plugs at different points to effectively constrain the medical device against movement within the channel, the trays must be highly customized for specific medical devices to locate the walls in the proper position for the plugs. Moreover, different sizes and configurations of plugs are required for diverse medical devices, and the walls must be specially configured in accordance with the plugs being utilized. A single tray usually cannot be employed for diverse medical devices and plugs, and conventional blister containers are thusly limited. Additionally, the blister container holding the medical device is frequently sterilized by gas or radiation sterilization techniques after the backing sheet has been sealed thereto; however, the plugs commonly shrink relative to the walls during sterilization negating any benefits derived from the walls in restricting movement of the plugs within the channel. Another disadvantage of conventional blister containers is that the plugs holding discrete parts of the medical device allows unsupported parts of the medical device remote from the plugs to move within the channel. Such movement is particularly likely when the medical device is made from a flexible material and can structurally impair the medical device.